1. Field
The present disclosure relates to a bulk acoustic wave resonator and a filter including the same.
2. Description of Related Art
In accordance with the recent rapid development of mobile communications devices, chemical and biological devices, and the like, demand for small, lightweight filters, oscillators, resonant elements, acoustic resonant mass sensors, and the like has increased.
As a means for implementing such small, lightweight filters, oscillators, resonant elements, acoustic resonant mass sensors, and the like, a bulk acoustic resonator has commonly been used. Such a bulk acoustic resonator has positive attributes in that it may be mass-produced at a minimal cost and may be subminiaturized. Further, the bulk acoustic resonator has advantages in that it may implement a high quality Q factor, a main property of a filter; may be used in a micro-frequency band; and may particularly be implemented in bands of personal communication system (PCS) and digital cordless system (DCS).
Generally, the bulk acoustic resonator has a structure including a resonating part implemented by sequentially laminating a lower electrode, a piezoelectric layer, and an upper electrode on a substrate. When an electric field is maintained in the piezoelectric layer by applying electrical energy to the lower and upper electrodes, the electric field causes a piezoelectric phenomenon in the piezoelectric layer, thereby causing the resonating part to be vibrated in a predetermined direction. As a result, an acoustic wave is generated in the same direction as the vibration direction of the resonating part, thereby causing resonance.